DTS or AC3?

[rondari]

Hi,

some people may have noticed my previous thread, asking people to go and check out some of the DTS surround sound files on www.ambisonia.com ... about which there was no discussion.

The decision was made to go with DTS as opposed to AC3 because DTS files can be burnt to CD (as stereo files), and can hence be easily downloaded, burnt to a CD and dropped into any DVD player connected to a surround amplifier.

But there seems to be a strong preference for AC3 files on doom9 ... and that makes me wonder _why_ .... can anyone give me any reasons why AC3 files are preferrable over DTS files?

I'm trying to identify which is the best format for online distribution of ambisonic surround sounds... should this be AC3 over DTS? (and if so, why?)

Etienne

[tebasuna51]

1) Better quality/bitrate (is a opinion of course).

2) Better compatibility. Not all standalone players have DTS decoder.

3) Don't exist a free DTS encoder.

[rondari]

1) Better quality/bitrate (is a opinion of course).

2) Better compatibility. Not all standalone players have DTS decoder.

3) Don't exist a free DTS encoder.

about 1) if I understand right, AC3 is capable of higher bitrates, but usually a lower bitrate is used (is this wrong?)

about 2) ... I understand that very few modern DVD players (hardware or software) are _not_ capable of playing back DTS

about 3) ... for AC3 there is ffmpeg and its fork Aften ... and these are probably fine for personal use, but are there not licensing problems using these? (I'm not sure). Fine for personal use but for a site with a devloping public profile, there might be eventual problems.

Etienne

[setarip_old]

Hi! I understand that very few modern DVD players (hardware or software) are _not_ capable of playing back DTSIt's not a question of the standalone players' ability to handle DTS, it's a fact that MOST users do not have the required AUDIO HARDWARE needed for DTS playback...

[honai]

Licensing costs used to be higher for DTS than Dolby Digital in the past, that's why there is less DTS content out there.

[rondari]

Hi!It's not a question of the standalone players' ability to handle DTS, it's a fact that MOST users do not have the required AUDIO HARDWARE needed for DTS playback...

what do you mean by AUDIO HARDWARE? do you mean the surround amplifier? To my knowledge practically all moderm surround amplifiers are capable of decoding DTS.

Other than a surround amplifier, the only other relevant audio hardware that I can see (where DTS might have different support compared to AC3) is sound cards ...

... but that's exactly my question .... how do most of the members on the doom9 forum play surround audio? ... is it via sound cards that output analog, via sound cards that output digital to surround amplifiers, via hardware DVD players, or other ...

etienne

[squid_80]

what do you mean by AUDIO HARDWARE? do you mean the surround amplifier? To my knowledge practically all moderm surround amplifiers are capable of decoding DTS.
I think what he meant was the average joe probably doesn't have a surround amp, just a dvd player with analog outputs connected to the tv. Practically all DVD players can decode AC3 and output it via analog but if it's DTS they'll only output digitally and a separate decoder/amp is required.

[rondari]

... Practically all DVD players can decode AC3 and output it via analog but if it's DTS they'll only output digitally and a separate decoder/amp is required.

hmmm .... are you saying that DVD players will spit out analog stereo of an AC3 stream, but cant do that with DTS?

hence making AC3 more accessible to those who dont have surround amplifiers?

[honai]

Many DVD players can't decode DTS at all, yes.

[Arite]

It is a requirement for a DVD-Video complient DVD player to be able to decode AC3 audio, as that is one of the Mandatory audio codecs - along with LPCM. DTS, however, is a Optional codec, with only a few DVD players actually having built-in hardware decoders.

An average DVD player might have a DTS logo on it, which often means it will stream the raw DTS sream to e.g. a surround sound system via S/PDIF. Raw AC3 audio will also be able to be sent via S/PDIF to an external decoder. This is good if you have an external amplifier/surround system which can decode DTS. If you don't have an external amplifier at all then you can still listen to the AC3 audio via e.g. a TV (downmixed to stereo) as the DVD has a built in AC3 decoder. There are very few DVD players that are able to decode DTS natively - often require an external decoder.

In addition, not all surround system can decode DTS either - so of the lower priced one are only capable of decoding AC3 audio.

There is currently only one open source decoder library for DTS (by DTS I refer to just the DTS Digital Coherant Acoustics part), libdca (VideoLAN). However, this does enable many potential mathod of listening to DTS audio without the need for an expensive hardware decoder. For example, DTS could be decoded in VLC media player and streamed out of a S/PDIF out port as decoded LPCM straight into an amplifier or surround sound system.

If "quality per bit" was relevant, then AC3 would win, as the compression algorithm is a lot more efficient that that of DTS. DTS used a ADPCM style compression algorithm which works by reducing the quantization-steps (uses vector quantization) in order to reduce the bitrate. This is relatively simple in comparision to the large amount of processing required to encode/decode AC3 audio, and so is less tasking on the CPU. The resultant file size is much larger, however is considered to be higher quality as it has undergone less processing and compression, which is why it is favoured by many audiophiles.

DTS-CDs (DTS-WAV - DTS at 44.1kHz encapsulated in a WAV file, for CDs) are not that easy to play either - to playback a DTS-WAV CD one needs a CD-player that is able to detent and decode the stereo "noise" into 6 LPCM channels.

As tebauna51 rightly said, there is no free DTS encoder available - not even any low-costing commercial pieces of software. This is due to the large patents placed on DTS and higher licensing costs.

Nevertheless - the question is who the ambisonic audio is aimed at - if it is aimed at someone who had a proper surround sound system set-up then it is likely that they would be able to playback DTS audio as well. If it just aimed at someone who wishes to play it back on a DVD player (in stereo), then AC3.

Cheers, Arite.

[Mug Funky]

ac3 is much more efficient than DTS. it's only failing point as far as quality (assuming bitrate is sufficient - 448 and above for 5.1) is transients and impulsive audio. and i believe (haven't tested it yet) aften should handle this stuff pretty well and possibly better than most commercial encoders.

DTS is actually quite primitive. it's on par with mp2 as far as encoding features go, only it has less subbands and therefore ends up lowpassing more than it should (so you lose high freqs unless they're really loud). it's minimum bitrate is 754.5 kbps, and it's nominal bitrate is 1509 kbps, plus padding to get it up to the bitrate of regular 16/44.1 audio.

even if DTS had a free encoder, licensing will be just as big if not bigger a problem than ac3. they're both heavily "commercial" codecs. the only time licensing isn't an issue is when you're glass-mastering DVD discs, as the licensing fee is covered in the per-disc price. i dare say distributing either of these codecs online could be a problem, but i'm not a lawyer and wouldn't want to make any claims i can't back up.

a lot of people comment that the DTS track sounds more open, dynamic, insert-placebo-word-here when compared to the ac3 track on the same disc. i say that's because (a) the DTS track doesn't get DRC'd inside the DVD player like ac3 does (ie 1 less feature for DTS), and (b) 9 out of 10 times, the DTS track is a completely different mix, on a different master tape.

[rondari]

thanks for the information ..... I'm starting to understand the implications of using the different codecs.

As Arite says, which codec is best depends on the target market.

In the case of ambisonia.com, we are targetting surround sound users only ... there isn't too much point in people listening to the recordings in stereo... so in that sense DTS is fine.

DTS also has the advantage of the DTS-CD format... where people can burn the tracks as audio CD's and play them back on a DVD player with a digital connection to a surround sound system

What worries me is the licensing ... but as Mug Funky states, I guess I would need to consult a lawyer...

All that said ... it sounds like the decision is between:

"oh, why wont this disc play in my DVD player connected to my TV", (DTS)... and

"this disc works well in my DVD player ... but its stereo not surround"...(AC3).

Something else to note is that I get constantly conflicting reports about codec quality.

Etienne